1. Field of the Invention
The present invention relates to a diffusion system having an air curtain formation function for manufacturing semiconductor devices and a method of controlling the same, and more particularly, to a diffusion system having an air curtain formation function for preventing the loss of the heat inside the diffusion furnace by cutting off the loss of the heated air flow, and a method of controlling the same.
2. Background of the Related Art
Generally, semiconductor devices are manufactured by carrying out various fabrication processes repeatedly, and there are many types of main facility systems and supplementary facility systems for preforming these processes.
Among the various processes, a diffusion process includes an oxidation step for forming an oxide layer, and an annealing step for activating or stabilizing impurities such as boron (B) or phosphorus (P), which are implanted to provide electrical characteristics, etc.
The main facility system for the diffusion process is a furnace, which comprises a quartz tube and a heating chamber including a heater to heat the quartz tube; and the furnace has an opening for entry and removal of wafers.
In addition, a supplementary facility system for the furnace includes a process gas supplying unit for supplying a certain amount of process gas into the chamber; a boat elevator for loading/unloading a wafer boat having a plurality of wafers therein to the furnace; a wafer transfer unit for loading/unloading the wafers to the wafer boat; and a controlling unit for controlling the above components mechanically, etc.
After the wafer boat is loaded into the furnace through the opening, and the diffusion process is completed, the wafer boat is unloaded from the furnace through the opening, and the wafers loaded in the wafer boat are moved into a wafer transfer apparatus, such as a cassette, which will be moved to another fabrication system for a subsequent process.
Then, additional wafers to be processed are loaded into the wafer boat, the wafer boat is loaded into the furnace through the opening, and the diffusion process is carried out inside the furnace.
Generally, the furnace is continuously heated to maintain a constant temperature inside while the wafer boat is loaded or unloaded through the open opening. In addition, heaters are installed in some sections inside the furnace (e.g., upper section, middle section, lower section) to heat each respective section inside the furnace separately and maintain a uniform temperature throughout all sections. In addition, to control the temperature of the heater in each section of the furnace, there is provided a thermocouple (T/C) in each section inside the furnace.
However, in the conventional furnace, heated air flows out of the furnace through the open opening while the wafer boat is loaded/unloaded and the wafers therein are transferred, so that a large amount of heated air flow is lost through the opening, and the temperature uniformity is seriously deteriorated around the opening of the furnace. As a result, non-uniform thickness layers are formed on the semiconductor substrate due to the deteriorated temperature uniformity.
Therefore, in an effort to solve the problem, the temperature of the heater around the opening is raised to compensate for the temperature drop around the opening due to the flow of heated air through the opening. Alternatively, a cut-off door is installed to close a portion of the opening when the wafer boat has completely exited the furnace.
However, the conventional methods used to raise the temperature of the heater around the opening results in deterioration of the inner resistance of the heater, and a large amount of heat energy is still wasted because the loss of heated air is not prevented. Also, time is lost in compensating for the loss of the heated air flow and raising the inner temperature around the opening during the diffusion process.
In addition, while a cut-off door may close the opening and shut off the heated air flow coming out of the furnace while the wafer boat is completely removed from the opening, it cannot shut off the heated air flow while the wafer boat is being loaded or unloaded through the opening. In addition, the cut-off door is designed in a non-contact manner in order to prevent the generation of particles, and therefore, it can only partially shut off the heated air flow even when the cut-off door is in the closed position. Therefore, the cut-off door fails to stop the flow of heated air out of the furnace.